This invention relates to a phosphor, and more particularly to a phosphor having a pigment of a specific color added thereto in order to extract a specific wavelength from luminous colors.
A phosphor containing 15% of CoAl3O4 acting as a blue pigment and 85% of ZnO:Zn acting as a phosphor material which are mixed each other is known in the art as disclosed in Japanese Patent Application Laid-Open Publication No. 71982/1983. The phosphor disclosed exhibits a luminous color shifted to a side of a blue color as compared with a phosphor consisting of only the ZnO:Zn phosphor material.
The conventional phosphor described above was subjected to a high-temperature operation test. As a result, unfortunately it was found that the high temperature operation causes the non-driven phosphor or phosphor which was not driven for luminescence during the operation to be highly deteriorated to a degree of failing to permit the phosphor to be put to practical use.
More specifically, in the high-temperature operation test, the phosphor was continuously subjected to the test for 20 hours in an atmosphere at 85xc2x0 C. and then luminance retention (L level) of the phosphor was measured after the test. As a result, supposing that initial luminance of the phosphor is 100%, the driven phosphor or phosphor which was driven for display or luminescence exhibited an L level of 90% or more which is above a standard level of 80% or more. However, the non-driven phosphor which was not driven for luminescence or subjected to luminescence during the test exhibited an L level as low as 50% below the standard level. The term xe2x80x9cphosphor which was not driven for luminescencexe2x80x9d, xe2x80x9cphosphor which was not subjected to driving for luminescencexe2x80x9d or xe2x80x9cnon-driven phosphorxe2x80x9d used herein indicates the phosphor which was not continuously driven for luminescence during test period over, for example, 20 hours in the test. Instead, the non-driven phosphor was driven for luminescence after a lapse of the test time and then luminance retention thereof was measured.
The inventors considered reasons why the non-driven phosphor is reduced in luminance. First, it was supposed that a deterioration in the non-driven phosphor is due to the fact that any substance is discharged from the phosphor being driven for luminescence (driven phosphor) due to impingement of electrons thereon and then adhered to the non-driven phosphor. In order to ascertain whether such supposition is correct, it was examined whether a blue pigment added to the phosphor contains any substance which is apt to be outwardly discharged therefrom. As a result of various attempts, the following fact was found. More particularly, 1 g of the blue pigment was added to 70 g of pure water to prepare a mixture, which was then stirred to obtain a solution. Then, the amount of a sodium ion (Na+) in the solution was measured by means of a pH meter. As a result, the sodium ion was detected in an amount of 80 to 90 ppm even when the blue pigment was added to pure water after being washed. This would be due to the fact that the pigment readily causes liberation of Na+ because in general the pigment is alkaline and contains plenty of Na. Thus, when the ZnO:Zn phosphor having the pigment mixedly added thereto is driven for luminescence in the high-temperature test, electrons impinged on the driven pigment causes Na+ to be emitted therefrom, resulting in the Na+ being adhered to the non-driven phosphor. This leads to a deterioration in the non-driven phosphor.
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention to provide a phosphor which is capable of preventing a deterioration in luminous characteristics of the phosphor, particularly, high-temperature operation characteristics thereof due to a pigment contained therein.
In accordance with one aspect of the present invention, a phosphor is provided. The phosphor has a neutral pigment adhered thereto.
In a preferred embodiment of the present invention, the neutral pigment is prepared by melting a mixture obtained by adding SiO2 to an alkaline pigment.
In a preferred embodiment of the present invention, SiO2 is added to the alkaline pigment in an amount of 0.1 to 10 wt. % based on the alkaline pigment.
In a preferred embodiment of the present invention, the phosphor is selected from the group consisting of a ZnS phosphor, a ZnCdS phosphor, and a ZnGa2O4 phosphor. The alkaline pigment is selected from the group consisting of Tixe2x80x94Sbxe2x80x94Ni, Coxe2x80x94Alxe2x80x94Crxe2x80x94Ti, Tixe2x80x94Znxe2x80x94Nixe2x80x94Co and Coxe2x80x94Al.
In accordance with this aspect of the present invention, a phosphor is provided. The phosphor has a pigment having a surface coated with glass added thereto.
In accordance with another aspect of the present invention, a fluorescent display device is provided. The fluorescent display device includes the phosphor described above.